Limb Length Discrepancy
Children are sometimes born with one limb longer than the other. Limb length discrepancies can also develop in childhood due to injury or infection to the growing ends of long bones. Although any of the long bones may be involved, the thigh and shin bones are frequently affected and can result in a limp. Limb lengthening is a surgical procedure to increase the height of the shorter limb to achieve symmetrical growth and improve gait and function.
In children, growth occurs near the ends of the long bones at areas of cartilage called growth plates. Conditions such as fractures, infection, bone diseases, joint inflammation and certain neurological conditions may affect the rate of growth at these regions causing a limb length discrepancy. Some of these conditions are present at birth while others develop during childhood. Limb length discrepancy can cause difficulties with walking which can lead to fatigue, low back pain and an increased risk of injury.
Your doctor will assess your child’s gait, measure the difference in limb length and predict how much this discrepancy will increase over time. This is done by assessing the health of the growth plates and the remainder of growth expected based on your child’s age and the location of the growth plate. Treatment is planned based on these assessments.
If the discrepancy is minimal, your doctor may recommend using a shoe lift to help your child walk better. In mild to moderate cases, a procedure to limit growth of the longer limb is performed to help the shorter limb catch up. For discrepancies greater than 3-4 cm, your doctor will usually recommend limb lengthening surgery to help your child achieve normal growth and function. With limb lengthening surgery, the bone can gradually be lengthened up to 15-20 cm
Limb lengthening may be accomplished by external or internal methods. During the procedure, other bone abnormalities may also be corrected.
Limb lengthening surgery is performed under anesthesia. Your doctor cuts the bone at the level of the metaphysis, a part of the bone that lies close to the growth plate and forms new bone at a faster rate. For the external method, a scaffold-shaped device called an external fixator is applied around your child’s leg and connected to the two bone segments with pins and wires. Alternatively, a unilateral external fixator may be used. The device is used to manually distract or pull apart the bone segments in periodic increments so that new bone grows at the defect. Skin and soft tissues around the bone gradually adapt to the new bone length. Distraction begins approximately a week after surgery. Your surgeon will show you how to adjust the device for distraction and how often it is to be performed. Distraction should be gradual so that the limb grows at a rate of 1 mm a day or around 1 inch a month and the tissues are able to adapt appropriately without complications.
For previously injured bones or bones with poor vasculature the bone is lengthened at a slower rate. While using an external fixator, you will be instructed to carefully clean the area where the pins and wires pass through the skin to prevent infection. After the bone is adequately lengthened, the external fixator will continue to be worn until the bone is strong enough to support your child’s weight and activities.
For the internal method, your doctor cuts through the bone of the shorter limb and inserts a rod in the central cavity of the bone. The rod expands by itself gradually as the limb is moved. This distracts the bone segments stimulating new bone growth. The rod also helps the bone grow in proper alignment. Newer systems involve rods that are lengthened by a magnetic or automatic motorized mechanism. As an external fixator is not required, the chances of infection are reduced.
Treatment using the external or internal techniques takes several months to complete. Your child will need to visit the doctor regularly and participate in physical therapy to strengthen the bones, improve movement and help the soft tissues adapt to the bone lengthening.
Advantages & Disadvantages
With the external method, the rate of bone growth is well controlled, but there is an increased risk of infection through the pin sites.
The internal method has a lower risk of infection, but bone growth may not be as well controlled.
Risks and Complications
Distracting the bone segments too quickly can result in nerve and blood vessel damage.
Bone lengthening may occasionally result in stiffness of the neighboring joints.